Welcome back Scientists!
September 20, 2015
Homework:
Agenda
1. #motivationalmonday
2. Condensation
3. Freezing
4. Melting
Objective: Freezing/Melting; I will be able to explain on the
molecular level why a low enough temperature can cause the water vapor in air
to condense to liquid water and then freeze to form ice.
#motivationalmonday
Evaporation Animation
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson2#evaporation
Adding energy to the water on the paper towel increases
the motion of the water molecules. When the molecules
have enough energy, they can move fast enough to break
away from the attractions holding them to other molecules.
Take It Further
The wet paper towel was not heated. Why did
the water evaporate?
Take It Further
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson2#models_of_water_molec
ules
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson2#models_of_water_molec
ules
Condensation
Which cup has the most moisture on the outside of it?
Why do you think the cup that is exposed to more air has
more water on the outside of it?
Some people think that the moisture that appears on the
outside of a cold cup is water that has leaked through the
cup. How does this demonstration prove that this idea is
not true?
Condensation
It’s the opposite of evaporation. A gas changes
state to become a liquid.
What are some examples of condensation?
Condesation Animation
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson3#condensation
Since the water molecules were all separated
as a gas, why did they come together to form a
liquid?
Take It Further
Fogging up a cold window
When you breathe out, there is water vapor in your breath. When you
breathe on a cold window in the winter, the window gets tiny droplets of
moisture on it or “fogs up.” What happens to the molecules of water
vapor as they get near the cold window?
The water molecules in your breath are the gas water vapor. They slow down
as they transfer some of their energy to the cold window. The attractions
between the slower-moving water vapor molecules bring them together to form
tiny droplets of liquid water.
Take It Further
Warm breath in cold air
When you breathe out in the winter, you see “smoke,” which is really a
fog of tiny droplets of liquid water. What happens to the molecules of
water vapor from your breath when they hit the cold air?
The water vapor in your breath is warmer than the outside air. The water vapor
molecules transfer energy to the colder air. This makes the water vapor
molecules move more slowly. Their attractions overcome their motion and they
join together or condense to form liquid water.
Take It Further
Evaporation and condensation in the water cycle
One common place you see the results of evaporation and condensation
is in the weather. Water vapor in the air (humidity), clouds, and rain are all
the result of evaporation and condensation. What happens to the water
molecules during the evaporation and condensation stages of the water
cycle?
Freezing
Ice Bomb
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson4#ice_bomb
Why do you think freezing water in the metal container caused it to burst?
Why are roads likely to develop potholes during cold winters?
What do you think happens to water molecules when liquid water changes to
solid ice?
Ice Structure
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson4#ice_structure
Ice At Different Angles
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson4#ice_at_different_angles
Ice vs. Water
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson5#ice_and_water
Fill out the chart to compare how the molecules move in
water and ice. Select one of the options in each row and
write it under “water” or “ice” in the chart.
Freezing Point
The temperature at which a substance freezes is called
the freezing point.
The freezing point of water is 0 °C (32 °F). Corn oil and
isopropyl alcohol have lower freezing points than water.
This means that they need to be cooled to lower
temperatures to make them freeze.
Why do you think different liquids have different freezing
points?
Liquid Nitrogen
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson4#liquid_nitrogen
Frost
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson4#frost
http://www.snowcrystals.com/science/science.h
tml
Melting
Ice Melting on Different Surfaces
http://www.middleschoolchemistry.com/multimedia/chapter2/lesson5#ice_melti
ng_on_different_surfaces
Where do you think the energy came from to melt the ice?
What do you think happened to the speed of the molecules in
the ice when it was heated?
Melting Ice
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson5#melting_ice
Melting Ice
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson5#ice_and_water
How did the motion and arrangement of the water
molecules change as the ice melted?
State Changes
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson5#states_of_matter
States of Water
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson5#states_of_matter
How are the state changes of water similar to the state
changes in most other substances?
How are state changes of water different from the state
changes in most other substances?
Dry Ice
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson5#dry_ice
Dry Ice in Water
http://www.middleschoolchemistry.com/multime
dia/chapter2/lesson5#dry_ice_in_water
https://www.youtube.com/watch?v=KGqWeZm-LA